It brings to mind my husband's view of what's a 'deadly' knife, versus my view.
He came home from a trip once and I had had a particularly uneasy week with him being away. He was stunned to see a 2" paring knife sitting by the bed, and asked why on earth I would take such a measure. I said, "well, with no guns in the house it just made me feel better to have it at hand."
He stated his preference for one of the longer bladed butcher knives for self defense. I looked at him and scoffed, explaining that the longer the blade, the more likely that it would snap. A short, stocky blade allows for repeated stab and twist without the same risk of bending and snapping.
His jaw just sort of dropped. He felt I'd really given it a scary amount of thought. 8O
But in my take on it, you'd really need to register any knife over an inch long.